The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefor.
(1) Field of the Invention
The present invention relates to a tow cable termination assembly providing the termination and interface between an electro-optical tow cable and a towed array, or other towed optical system, and more particularly to a distributed tow cable termination assembly.
(2) Description of the Prior Art
Use of a towing cable to tow an array is a well known and acceptable element of a sonar system. The cable typically includes a core of optical fibers and/or electrical conductors housed within a protective jacket. One end of the cable supports the towed system (or array), the opposite end being the strength member termination area. Due to its operating environment, mechanical difficulties have been encountered with prior art towing cables. For example, synthetic fibers having high strength-to-weight ratios have been used for conventional tow cable termination assemblies (for example, Kevlar(copyright) fiber available from DuPont, Vectran(copyright) fiber available from Hoechst-Celenese, and Spectra(copyright) fiber available from Allied Signal), but the use of such fibers has not always met with success. In particular, the design parameters for a conventional tow cable requires that the synthetic fiber be used as the strength member, and special lightweight materials be used throughout. Conventional termination designs provide termination efficiencies (defined as the ratio of termination break strength to cable strength) of about 30% to 50% when utilizing these synthetic fibers. However, the requirements for the next generation tow cable termination assembly is in excess of 70%.
In addition, a second requirement for the termination assembly is to provide a seal against seawater intrusion into the core of the cable which can result in failure. Due to the higher incident of elongation, or stretch, of the fiber strength member in the tow cable (in comparison to a steel cable), failures have occurred in the seal area due to incidents of seawater intrusion. The seawater intrusion primarily results from the ineffectiveness of current seal designs to prevent leakage when the fibers become elongated and the core moves independently of the strength member. Conventional designs utilize a single o-ring as a secondary seal and do not protect against seawater intrusion through epoxy injections tubes if the primary seals fail.
Another issue associated with conventional termination assemblies is that they degrade over time in terms of strength and seal capability, because of the nature of the synthetic fibers, and the need to reel the cable around a winch during use. For example, the forces applied to the termination assemblies during use can result in a strength loss in the termination. This has been found to be especially true with towed array thin line handling systems that use 36xe2x80x3 diameter, multiple groove sheaves for handling the cable. Additionally, there have been problems associated with breakage of fibers and wires in the transition area between the tow cable termination assembly and the towed system. The use of synthetic fiber increases this problem and has been found to be a very difficult design issue. The changes in the stiffness between the cable and the towed system or device can also cause significant damage to the termination and the cable. The termination assembly is required to meet all strength and environmental specifications for their operating life which is expected to be typically about 3-5 years and includes numerous handling and deployment evolutions. Conventional designs do not support these requirements.
Accordingly, there is needed in the art a tow cable termination assembly having an improved operating life and which is cost effective, reliable and easy to manufacture.
The present invention is directed to a distributed fiber strength member tow cable termination assembly (DTCTA) having a strength member termination area which is spaced from a signal conductor termination area, and further includes a seal area having a plurality of sealing members. The strength member termination area preferably includes a strength member termination wedge having a curved outer face which allows for higher termination efficiency. The strength member termination area and signal conductor termination area are distributed, or separated, by a predetermined distance by, for example a length of hose. In one embodiment, epoxy is fed through holes located inside the primary seal area into the termination wedge. A secondary seal area including a plurality of stacked seals, for example V-cup seals, are also disposed behind the primary seal. The DTCTA further supports all hydrodynamic tow loads applied by the towed system and transfers the data and power over the electro-optical core, as is known in the art.